The bitter war of words contrasts with last year's Westminster election when the two parties formed pacts in four constituencies, including Mr Dodds' own in North Belfast.

However, Mr Dodds has characterised Mr Nesbitt as "a man that blows with the wind".

But the Ulster Unionist boss called that "water off a duck's back" and said he remained proud the parties had come together for the House of Commons battle last year.

"I understand the DUP revert to bashing fellow unionists at election time, particularly when they perceive the Ulster Unionist Party to be a threat," he said.

"I remain proud I persuaded the DUP of the merits of my strategy this time last year to secure a return to the position where the majority of Northern Ireland's MPs are pro-Union.

"At that time, the DUP responded with nothing but pro-DUP proposals. I regret the DUP are currently choosing to attack the Ulster Unionist Party at every turn."

His counter-attack came after Mr Dodds issued a statement arguing: "Mike Nesbitt has always been known as a man that blows with the wind. All spin but no substance."

Referring to an hour-long interview Mr Nesbitt had on BBC Radio Ulster's The Stephen Nolan Show, the veteran DUP man said: "He was exposed as not being across detail, as having no plan for Northern Ireland and as having performed a political somersault on re-entering the Executive."

Mr Dodds said it had become clear the UUP's withdrawal from the Executive last year "was nothing short of a political stunt without an ounce of principle. It was a shameful tactical device to try and exploit people's fears."

The Ulster Unionists removed their only minister from the Executive in the wake of the murder of Kevin McGuigan in east Belfast last August.

Later that month, the UUP decided to withdraw Regional Development Minister Danny Kennedy from the Executive after the police said members of the Provisional IRA were involved in the McGuigan murder.

Mr Nesbitt said at the time that Sinn Fein's denials that the IRA still exists, had a command structure, and had members still involved in murder meant his trust in the republican party had been so badly damaged, his party could no longer share power with them.

However, the UUP was criticised after its manifesto launch for not putting pre-conditions on Sinn Fein's position on the IRA in order for Mr Nesbitt's party to re-enter the Executive.